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Biomedical subjects

Y Tan

Publications and source records attributed to Y Tan.

At least 163 records · Page 9Linked to original sources
PubMed1996

[Histopathological and immunohistochemical studies on medullary thyroid carcinoma].

In order to study the multidifferentiation of medullary carcinoma of the thyroid gland (MCT), 24 cases of MCT were examined for the presence of immunoreactive calcitonin (CT), thyroglobulin (Tg), chromogranin A (CgA), somatostatin (SS), serotonin (5-HT), S-100 protein (S-100), neuron-specific enolase (NSE), vasoactive intestinal polypeptide (VIP), adrenocorticotrophin (ACTH) and neurofilament protein (NF) by using immunohistochemical ABC methods. Results showed that CT-immunoreactive cells were present in all tumors. Tg was present in three tumors. 23 cases contained CgA-immunoreactive cells. 14 tumors contained 5-HT-immunoreactive cells, 10 cases were immunoreactive to NSE and SS. 4 tumors contained VIP-immunoreactive cells and only one cases was positive for S-100. The demonstration of immunoreactivity for multiple antigens in 24 cases suggests that the origin of medullary thyroid carcinoma may originate from neuroectoderm cells potentially capable of producing numerous hormone substances. In addition, as the neoplastic cells in 12% of the tumors containing hormone substances as well as thyroglobulin, it is suggested that follicular epithelial differentiation and mixed medullary thyroid carcinoma may be more common than previously suspected. Recent studies indicate that mixed carcinoma of the thyroid may be derived from common stem cells in posterior branchia capable of differentiating into both follicular and parafollicular tumor cells.

Adult↗
PubMed1995

Purification and characterization of an AP endonuclease/DNA 3' repair diesterase from mouse ascites sarcoma cells.

Purification and characterization of a DNA repair enzyme having 5' apurinic/apyrimidinic (AP) endonuclease activity are reported. The enzyme extracted from mouse ascites sarcoma (SR-C3H/He) cells with 0.2 M potassium phosphate buffer (pH 7.5) was purified by successive chromatographies on phosphocellulose, DEAE-cellulose, phosphocellulose (a second time) and single-stranded DNA cellulose, and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified enzyme has an apparent molecular mass of 30 kDa as determined by SDS-PAGE. It was shown to have nicking activity on acid-depurinated DNA but not on intact DNA, and to have priming activities for DNA polymerase on acid-depurinated DNA and bleomycin-treated DNA. The results indicate that it is a multifunctional DNA repair enzyme having 5' AP endonuclease and DNA 3' repair diesterase activities. The enzyme activity is dependent upon the presence of a divalent cation such as Mg2+. Its amino-terminal amino acid and internal amino acid sequences are determined.

Animals↗
PubMed1995

Morphometric analysis of ventral mesencephalic neurons retrogradely labeled with Fluoro-Gold following injections in the shell, core and rostral pole of the rat nucleus accumbens.

Morphologically distinct subsets of mesotelencephalic neurons were sought following retrograde transport of Fluoro-Gold from iontophoretic injections relatively restricted to the medial shell, core or rostral pole subterritories of the nucleus accumbens. The diameter and lengths of Fluoro-Gold immunolabeled dendrites of medial shell-projecting neurons were less than those of core and rostral pole-projecting neurons.

Animals↗
PubMed1995

Analysis of enzymatic DNA sequencing reactions by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

The products from base-specific, dideoxy-nucleotide chain-termination DNA sequencing reactions catalyzed by the modified T7 DNA polymerase have been analyzed by using the technique of matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. Preliminary experiments were performed to determine detection limits for a synthetic mixture of mixed-base single-stranded DNA which contained a 14-mer, a 21-mer, and a 41-mer; acceptable spectra, showing peaks for each component, were obtainable for samples that contained as little as 5 fmol per component. Initial sequencing reactions were therefore carried out on 2-pmol amounts of a short synthetic template that was 45 nucleotides in length, employing 2 pmol of 12-mer as the primer strand. This provided readable sequence information out to the 19th base past the primer. Using a 21-mer primer, nearly the entire sequence of the template could be read.

Base Sequence↗
PubMed1995

The emergence of a highly transmissible lineage of cbl+ Pseudomonas (Burkholderia) cepacia causing CF centre epidemics in North America and Britain.

The rapid increase in Pseudomonas (Burkholderia) cepacia infection in cystic fibrosis (CF) patients suggests epidemic transmission, but the degree of transmissibility remains controversial as conflicting conclusions have been drawn from studies at different CF centres. This report provides the first DNA sequence-based documentation of a divergent evolutionary lineage of P. cepacia associated with CF centre epidemics in North America (Toronto) and Europe (Edinburgh). The involved epidemic clone encoded and expressed novel cable (Cbl) pili that bind to CF mucin. The sequence of the cblA pilin subunit gene carried by the epidemic isolates proved to be invariant. Although it remains to be determined how many distinct, highly transmissible lineages exist, our results provide both a DNA sequence and chromosomal fingerprint that can be used to screen for one such particularly infectious, transatlantic clone.

Amino Acid Sequence↗
PubMed1995

[Research on rectal administration of bark of official Magnolia].

Fluorescence assay was applied to the determination of magnolol in rabbit blood, and the best way to administer the bark of official magnolia per rectal was established by orthogonal test. Then the two routes of administration were compared by AUC of magnolol and per rectal was found better than P.O. In addition, the modified isolated rectum-bag method was applied successfully to the research on rectal administration of bark of official magnolia.

Administration, Rectal↗
PubMed1995

[Rectal administration of ash bark].

A TLC-densitometric method was applied to determine aesculin in rabbit blood. The best way for ash bark rectal administration was found by orthogonal design [L4(2(3))]. The two routes of administration (per rectal, P.O.) were compared by bioavailabilities and the result indicated that per rectal was better than P.O. Modified isolated rectum-bag method was applied successfully to finding the best way for rectal administration of ash bark.

Administration, Rectal↗
PubMed1995

The measurement and application of TSH-IRMA levels among different age groups in areas with iodine deficiency disorders.

Using immunoradiometric TSH assay (TSH-IRMA) to measure whole blood TSH levels spotted onto filter paper, we compared TSH levels among different age groups (neonates, < 1 yr infants, schoolchildren aged 7 to 14 yrs, adults, pregnant women and reproductive-age women) in Guiyang, where iodine deficiency has long been a problem. The results showed: 1) The percentage of subjects with TSH levels equal to or greater than 5 mIU/L in the neonate group was 38.9% while the percentages in the other groups were 0-3.3% (P < 0.01); 2) The TSH levels of the neonates were inversely related to the urinary iodine values of their mothers (pregnant women). (r = -0.5, P < 0.01); 3) 97.6% of the inhabitants in Guiyang ingested salt with less than 20 mg/kg iodine. The results indicate that iodine deficiency remains a problem in Guiyang. Neonates are the only ideal population for monitoring iodine deficiency.

Adolescent↗
PubMed1995

Morphological changes of myoepithelial cells of mouse lacrimal glands during postnatal development.

To reveal the correlation between myoepithelial cell configuration and size/shape of glandular endpieces (acini), we observed postnatal developmental changes of myoepithelial cells in the lacrimal glands of mice. Glandular and myoepithelial cells were examined in paraffin sections and in isolated acini. In newborns, rudiments of acini showed no clear lumina and glandular cells had few secretory granules. There were no myoepithelial cells with actin. At 3 days after birth, some rudiments showed lumina; however, secretory granules were not salient. Round cells in the periphery of the acini showed immunoreactivity for actin. In 1-week-old mice, glandular cells were polarized: luminal cytoplasm contained some secretory granules, and nuclei were located basally. Most myoepithelial cells were flattened and sometimes projected thin processes in various directions. At 2 weeks, the glandular cells increased their size and contained numerous secretory granules, and the myoepithelial cells were almost stellate. In 4-8 week-old mice, acini increased their size, and myoepithelial cells were very thin and processes were prolonged in length and increased in number. During postnatal development, their distribution of myoepithelial cells was more scarce, while the size of acini increased. This reciprocal relation of myoepithelial cell distribution and acinar size may indicate that the changes of myoepithelial cell configurations depend on the change of acinus size.

Animals↗
PubMed1995

[Effect of tetrandrine on pulmonary hypertension induced by monocrotaline in rats].

The effects of Tetrandrine (Tet) on intraacinous pulmonary arteries (IAPA) and bemodynamics were studied by means of a rat pulmonary hypertension model induced by monocrotaline. The results showed that Tet could reduce the contractive pressure of pulmonary artery, right ventricle and right atrium of heart by 28.0%, 28.3%, and 31.5% respectively. It could also decrease the vascular degeneration of endoepithelial cells of IAPA, the endoepithelial subcavity, the collagens of medial membrane and the numbers of smooth muscles of IAPA.

Alkaloids↗
PubMed1995

[Detection of estrogen receptor messenger ribonucleic acid in normal and ovariectomized rat bone].

Using ovariectomized female SD rats (OVX) as animal osteoporosis models, RNA samples were extracted directly from rat bone. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to examine the estrogen receptor (ER) messenger RNA (mRNA) level of expression in normal and OVX rat bone tissue. Results demonstrated that the rat ER gene is expressed in normal rat bone. DNA sequencing showed 300 bases sequence. We found that the OVX rats showed a sharp decrease in ER mRNA level when estrogen was reduced after ovariectomy and the expression of bone ER mRNA increased during estradiol therapy, suggesting that the expression of bone ER mRNA relies upon the level of estrogen. In addition, ER plays a very important role in the pathogenesis by means of its gene regulatory functions.

Animals↗
PubMed1994

Nucleotide polymorphism in colicin E1 and Ia plasmids from natural isolates of Escherichia coli.

We examined DNA sequence polymorphism for the colicin gene clusters of seven ColE1 and six ColIa plasmids obtained from natural isolates of Escherichia coli. These gene clusters harbor levels of nucleotide diversity ranging from 0.006 (ColIa) to 0.054 (ColE1). This level of diversity is similar to that observed for chromosomally encoded E. coli genes. However, the variance associated with these estimates is severalfold higher for the plasmid-encoded genes. This increased variance may be due to the differing plasmid population sizes. The pattern of colicin gene cluster polymorphism suggests that the two colicins are evolving in different fashions. ColE1 accumulates polymorphism at an elevated rate in the central domain of the colicin protein, while ColIa polymorphism is distributed evenly along the gene cluster. Comparison of the patterns of divergence between colicin and related proteins of ColIa and Ib and patterns of polymorphism within ColIa suggest that this gene cluster is not evolving in a neutral fashion. These data lend support to the hypothesis that colicin gene clusters may evolve under the influence of diversifying selection.

Bacteriocin Plasmids↗
PubMed1994

Ion-pair solid-phase extraction of cimetidine from plasma and subsequent analysis by high-performance liquid chromatography.

An improved method is described for the solid-phase extraction of cimetidine from plasma or serum with subsequent analysis by HPLC. New aspects of the method include protein precipitation with metaphosphoric acid (5%, w/v), followed by selective adsorption of cimetidine and the internal standard ranitidine on the surface of a solid-phase phenyl (PH Bond Elut) column, using octanesulfonate as an ion-pairing agent. Separation was achieved on a LiChrosorb RP-18 column with a mobile phase consisting of acetonitrile-0.01 M phosphate buffer pH 3.0 containing 0.005 M octanesulfonate (22:78, v/v). The intra-assay coefficient of variation varied between 0.7 and 4.0%. The procedure provides cleaner and more stable samples and a better recovery (90 +/- 2.3%) and sensitivity (limit of detection 5 ng/ml and limit of quantitation 25 ng/ml) as compared with previous methods.

Chromatography, High Pressure Liquid↗
PubMed1994

Comparison of the conformational stability of the molten globule and native states of horse cytochrome c. Effects of acetylation, heat, urea and guanidine-hydrochloride.

The molten globule state has been assumed to be a major intermediate of protein folding. We compared the stability of the native and acidic molten globule states of horse ferricytochrome c against heat, urea and guanidine hydrochloride (Gdn-HCl) using the intact species and species modified by various degrees of acetylation of the lysyl epsilon-amino groups. After acetylation, the amino groups cannot protonate at acidic pH. Thermal and urea-induced unfolding transitions measured by far-UV circular dichroism and differential scanning calorimetry showed that, whereas acetylation stabilizes the molten globule state at pH 2, it destabilizes the native state at pH 7, suggesting a difference in their mechanisms of conformational stability. On the other hand, the effects of Gdn-Hcl were remarkable. Contrary to what was expected from the thermal and urea-induced unfolding transitions, the Gdn-HCl-induced unfolding transition of the native state at pH 7 was insensitive to the extent of acetylation. At pH 2, Gdn-HCl at low concentrations stabilized the molten globule state and, at high concentrations, destabilized it. Consideration of the difference in the effects of Gdn-HCl from those of urea or heat indicated that, whereas the net positive charge repulsion destabilizes the molten globule state at pH 2, the local negative charge repulsion produced by acetylation of amino groups, and not the net charge, critically destabilizes the native state at pH 7. These results predict that, because of its ionic nature, Gdn-HCl will produce substantially different effects on the conformational states of some proteins compared with those of urea.

Acetylation↗